Telephone ringing system



' l R. s. BAILEY TELEPHONE RINGING SYSTEM Filed Feb. 9, 1925 2 Sheets-Sheet 1 LDUDUIJIJDDU by i wlw-' JAW.

Feb.. 9, 192e. 1,511,991

R. S. BAILEY TELEPHONE RINGING SYSTEM Filed Reb. 9, 1925 2 Sheets-'snee'vd 2 /m/enfor: Pand 5. Ba/Yey y W M12 Patented Feb. k9, 1926.

PATENT o FFiCE.

RAND. S BAILEK--MONTQf-iit NEW' JERSEY., ASSIGNOR T0 AMERICAN TELE- PHONE AND-TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

mnnninonnnmeme SYSTEM.

Applicatiii filed-February 9, i925. sei-iai No. 7.972.

To zZZ- 1li/wm t may concern." 'I l-Be it -knowngthatL RAND S. BAILEY, residing at l\/Iontclaii,in the county of Essen f and Sta-te of New Jersey, have invented cer,

tain Ii'nproveinents in Telephone Ringing Systems, of'wliich the following is aY specification. y ,y l

This invention relatesto telephone systenis and inore particularly'to a ringing systein whereinr an operator inay 'ring' onl a 'de'- sired line. f

An object of the inventionis'- to iinprove systeinsof-t'hischaracter. i

A feature of the invention resides in the provision ofI a -gr'oup'of keys coininon to a plurality of connecting circuitsfwhereby the* actuation of, one ofl said'keys*l causes the application ofringing. current to the calling end'of vthe connecting circuit and" the actu"- ation of aiiotherof said keys prevents 'the applicationof ringing'lcurreiit to the'connecting` circuit.

Heretofore, expensive and complicated ar- L rangements have been'provided byV ineans of which the coiii'iectinp,V circuit automatically diifei'entiatcd between anv ordinary subsci'ibersliiie and' a trunk'line whereby thej applicationr4 of ringing currentv tothe trunk line was prevented.` Inaccord'ance with the present invention, afstand-ard i'nethod of operation is inade possibley whereby a kevof Soniey nature is always operated regardless f of whether the line connected with it is a subscribersline or a trunk line, it only beinn` necessary'for theoperator to differen-l tiate between the keys tobe operated de pending on the character oftheline with which the connectingr circuit is connected.

The invention will be readilyunderstood from the following detailed description inade with reference to the accompanying drawings. 'i

In the drawings: 1'

Figure l shows' two substations A and B in a group having' access to a line'finder F, and a link circuit D ,terininating ina plurality ofinultiple answ:eringy i'acksat a tele-V phone exchange. The structure ofthe switch or line i'iiide'r is of the general type disclosed in the Patentr No. 972,8'74-13. Kugelinann- October 1,8, 1910. and is adaptedA in its pres-v In' the following description, the sub-` scriber at station A will be considered the callingI subscriber and any oner of the four parties on the line L the called subscriber.

The' subscriber at station AV to initiate a. callI reinoves the receiver froin the switchhoolc'whereupon a circuit is established eX- tendingfroin groui'ided' battery through the winding ofthe start relay 100, winding of the line relay 101, back Contact and righthand armature of cut-off relay 102, over the subscribers closed line loop, inner armature and back contact of relay 102 to ground. The start relay 100 is coininon to a group of ten lines.

Upon operating, the start relay 100 connects. at its contacts 104, ground tothe inswitch available for use. As indicated on the drawing' by the lead 105` tlieVin-start lead 103 is'adapte'd to be cut through t'o the next succeeding'switch if the first switchV is busy; i l

Assuni"inf;` the switch F to be free to haiidie the inconnu;r call, the stepping relay 106 now operates iii a circuit extendingl froin grounded battery through the winding` of rel'ay'105, armature and'v back contact ofthe verticall magnet 107, armature and back Contact ofthe rotary magnet 108, contacts 109 of the olf-normal switch 110. back contact and outerright-hand armature of the oii-'nornial relay 111` iii-start lead 103 to ground at the contacts 104 and armature of the start relay 100. As soon asthe stepping' relay 10G operates, the vertical magnet 107` operates rin a circuit extending froin grounded batterytlirough ythe winding of the vvertical magnet 107, back Contact and right-hand arinature of the transfer relay 112, front contact and armature of stepping relay 100, and thence to ground on the instart: lead 103 over the circuit hereinbetore traced. r.lhe vertical magnet 107 in operating raises the brushes ot the switch F one level, and in addition opens the circuit for the stepping relay 100. T he steliping relay .100 in releasing opens the circuit tor the vertical magnet 107, whereupon this magnet releases. Upon the rise of the switch brushes to the first level due to the operation ot the i'crtical magnet 107. the oil-normal switch 110 is actuated. whereupon the circuit for the stepping relay 100 is transferred from -ground on the in--start lead 103 to ground at the back contact and right-hand armature o1' the hunting relay 113.

The windingof the transfer relay 112 is .now connected through the commutator brush 111 to the tirst connnutator segment 115. It the called line is located on the .tirst lcrel ot' the switch or line finder F, the transter relay 112 will operate through the commutator segment 115 to ground at the contacts 11e and armature o1 the start relay '100. ln the event that the calling line is not located on the tirst level of the switch, the stepping relay 10G and the vertical mag net 107 will continue to operate alternately, to the ground at the back contact and armature ot the limiting relay 113, until the vertical magnet 107 has raised the brushes to the level in which the calling line is located, at which time the transfer relay 112 will operate through the grounded eonnnutator segment, and lock to the back contact ground on the hunting relay 113.

Upon operating, the transfer relay 112 Substitutes the rotary magnet; 108 for the vertical magnet 107 in the stepping circuit with the stepping relay 10G. `The stepping Arelay 100 and rotary magnet 108 will then operate alternately to cause the switch F to rotate its brushes in the particular level in search ot the calling line.

When the line relay 101 operated, it connected ground to the terminal 117 on the multiple bank. and as the rotary magnet 10S advances the brushes to this line, the huntingI relay 113 operates in a circuit extending 'from grounded battery. through the winding ot relay 113, outer lett-hand armature and back contact ot' ott-normal relay 111, brush 118. terniinal 117 to ground over 1Ihe trout contact and armature ot' the line clay 101.

Relay 113 in operating removes ground trom the rotary stepping circuit to prevent 'further rotation ot the brushes at switch F. At its armatures 119 and 120, relay 113 connects the tip and ring conductors ot the calling line to corresponding terminals ot the multiple jacks 130. 1%10, 150 and 100. ln attracting its armature 121, relay 113 closes through the sleeve conductor of the calling line.

Relay 122 now operates in a circuit extending from grounded battery through the lett-hand winding of relay 122, middle armature and back contact of cut-off relay 123, Jfront contact and armature 120 of relay 113, brush 124 and terminal 125 of switch F, over the closed subscribers line loop, terminal 126 and brush 127 ot' switch F, armature 119 and front contact of relay 113, back con tact and outer armature of relay 123 to ground through the right-hand winding of relay 122. The windings ot relay 122 are of low resistance and therefore, when this relay is connected to the calling line, thc ine relay 101 and the start relay 100 are ehuntcd, whereupon these relays release. Relay 122 in attracting its right-hand armature establishes obvious circuits for the line lamps 131, 141, 151 and 161 causing these lamps to be illuminated. At its lefthand armature relay 122 causes the slow releasing relay 128 to operate in a circuit extending from grounded `battery through the winding ot' relay 128, left-hand armature and front contact of relay 122, to ground at the front contact and righthand armature of relay 113.

Slow releasing relay 128 in operation provides an auxiliary holding circuit for relay 113 and an energizing circuit for theotlnormal relay 111, both ot which circuits are obvious. lclay 111 in operating locks to ground at the contacts 129 ot the oi normal switch 110, and will not release until the switch F is restored to normal. In attracting its outer right-hand armature relay 111 transfers the n-start lead 103 to the conductor 105 leading to the next switch so that should another subscriber such as B initiate a call, the second selector would :function to extend the call. At its inner left-hand armature relay 111 prepares a circuit for the release magnet. 132, the com pletion of which is etl'ected when the linuting relay 113 restores. At its outer let'thand arn'iature relay '111 opens the hunting lead, it now being noted that the hunting` relay 113 is held operated under the control ot the callingl subscriber.

An (nierator at the telephone exchange, upon notingl the illnniination ot one of the line lamps 131, 111. 151 and 161, and who is irce to answer the call, inserts the plug 200 associated with one ot her connecting circuits into the jack, such as 130, located at her position. whereupon a circuit is established extending from grounded battery, through the lower lett-hand winding ot repeating coil 201, winding ot supervisory relay 202, ring contacts oil. plug 200 and jack 130, front Contact and armature 120 of re lay 113, brush 1241, tern'iinal 125, over the closed subscribers line loop, terminal 120, brush 127, armature 119 and front contact of relay 113, winding of supervisory relay 133', tip. contacts oi:- jack 130y and plug. 200, to ground through the ,upper left-hand winding ot" repeating coil 201. Relay 133 operates in this circuit and establishes an v'obvious circuit for the cut-oit relay 123.

. and 161 to be extinguished.

Relay 202 also operates-inthe above traced circuit, preventing lthe illumination ot' lamp 204. at this time and connecting the listening relay 205 to the sleeveconductor oi tho cord, whereupon this relay operates in a circuit extending from grounded battery, through the winding of relay 205, normal make-before-break contacts of relay 206, armature and front contact ot' relay 202, sleeve contacts of plug 200 and jack 130, front con tact and armature 121 of-relay 113, brush 136 and terminal 135 ot sWitchF, winding ot the line cut-olf relay'1021to ground. Relay 205 in attracting its lower armature disconnects ground from the winding of the test relay 203 and inattracting its other armatures connects the operators telephoneset, indicated at O. T. to the talking conductors ci' the connecting lcircuit C. The

cut-oit relay 102 operates to the circuit above traced to cut ofti the subseribers line relay 101 from the calling subscribers line. UA1- though there is an apparent tendency for ak race at this time, between the listening ,relay 205 and test relay 203V (it being obvious that with relay 202 operated the test relay 203 may operate from grounded battery through the winding` ot' relay 205, normal make-before-break contacts ot relay 206, armature and frontA contact ot relay 202,

" armature 212 and back contact ofrelay 206, winding of test relayl 203 to ground at the back contact and lower armature ot re.- lay 205) relay 202 is made slow-to-release so that should relay 203 operate at this time and momentarily short-circuit relay 202, relay 202 will hold up until relay 205 operates to, open the circuitfor relay 203.

The operator now ascertains the details of the call from the calling subscriber and upon learning that a subscriber on the line L is desired, she makes the usual busy test on the line L, and finding the same idle, inserts plug 208 into the jack 207 of the desired line. As a result of the insertion of plug 208 into jack 207, relay 209 operates in a circuit extending from grounded battery through the winding of relay 209,`back contactfan'd right-hand armature of relay'210, sleeve contacts of plug 208l and jack 207 to ground. Relay 209 infattracting its armature 211 establishes an obvious circuit for relay 206, which relaythereupon operates. ln attracting its armature 212, relay 206 removes th-e Wind-ing of the test relay 203 from the sleeveconductor of the. answering end of the connecting circuit C'. At its armature 213, relay 20.6` locks up tothe sleeve of the callingend of the connectin-g circuit and at its armature 214 it opens the circuit for theV listening relay 205, whereupon this relay releases, disconnecting the operators telephone set from the connecting circuit, and also connectsy battery to the answering sleeve circuit tov hold the subscribers cut-ott' rela-y 102 operated. The current from this battery is not sufficient to operate the message register magnet 166. In attracting its armature 215, relay 206 closes its contacts 216 and 217 for purposeswliich will hereinafter appear.

Relay 218 now operates in a circuit ex,- tending from grounded battery, over the back contact and outer right-hand armature off relay 220, winding of relay 218, iilament of lamp 221, back vcontact and armature of relay 222 to ground at the contacts 216 and armature 215 of relay 206. The lamp 221 is` illuminated in thisV circuit. kRelay 218 in operating causes the charge relay 219- to operate over an obvious circuit, in order to prepare the message register, magnet 166 for operation. The magnet 166 automati-y cally Yoperates when a calledsubscriber answers, as will hereinafter appear.

The operation of relay 209 also` connected. the master ringing keys- MK1 common to the position, to the cord circuit.

vShould the calling subscriber requestv a party M connection, the operator actuates the key M, thereupon connecting ground to its contacts 237, 238, 239 and 242. 'At the contacts 237 a circuit is established from ground on the contacts 237, over the conductor 243, armature 244 and frontv contact ot' relay 209, Winding'ofv relay 245- to battery and ground. Relay 245 operates in this circuit and in attracting its two outer armatures removes the short circuit from the ring-back tone condensers 246 and 247. At its inner lower armature relay 245 locks in a circuit which may be traced from-grounded battery,

lli)

through the Winding, front contact and inner 249 and front contact of relay 209, windingV of relay 252 to battery and ground. lRelay 252'operates -in this circuit and -in attracting its right-hand armature locksy itself in, a circuitV extending fromA groundedbattery, through the Winding lofr-elay 252, front contact and right-hand armature ot relay 252, armature and back contact ol marginal relay to `tn'ound at the contact i216 and armature i315 oi relay o. At its inner lett-hand armature relay prepares a circuit i'or re lay S2M, which will be completed in the 'lollowing description. At its outer lel`thand armature relay :2 prepares a circuit tor the transmission ot a special code ot ringing current, as Will hereinal'ter appear. At the contar ot' hey lll a ci 'cuit is established :lroni ground, arniature 255 and lront contact of relay 209, through the .rindini;- of relay :fin to battery and ground. llelay i256 operates in this circuit and at its right-hand arniature'locks itself in the saine locking cir enit as hereinbe'lfore traced for relay lo. ,it its inner lett-leuntarmature relay Bao councets `ground to the ring conductor ot the -alling end ot the connecting' circuit C, and at its outer left-hand armature it prepares the tip side ot the connection tor the t'answ inission ot ringing' current. At the contacts 23S) ot' key M a circuit is established it'or the lett-hand Winding ot relay 2l() by Way ol.l the a rinature 259 and front contact ot relay 20S). .Relay ill() operates in thisl circuit and locks lhroun'h its rightdiand winding' to lground on the sleeve oi the calling end olf the con netting circuit C. l'lelay dit) in operating` opens the, circuit lor the start relay 20). which relay thereupon releases. it being' .nonv understood that the relay 45, 25u and 25;' are locked to ground at the con'act lo olf armature 215 ot' relay Quo.

lVhile the brush ot interrupter :25S is on a conducting segment, current lronr battery 25T lions over the conductor 5260, over the normal inal e-betorebrenlt contacts and Winding' olf relay 2li-i to ground at the front ernitaet and inner lett-hand armature ot' ren lay 252. ln attracting; its` rilgg'ht-hand arma-i ture relay lochs under the control ot' relay 253:2. special code ol ringing current now traverses a path extending ifroin the ringinnj current supply through the interruptcr :luth conductor :MSL troni' contar-l and einer lett hand armature ot relay 2ii2 lett-hand arinature and baci; contact oi relay iuu. winding' olE marginal relay 255i, outer le |`thand arniature and front contact ot relay 2:76. iront contact and upper armature ot' relay 24.3, tip contacts ot' plug 20S and jack 20T to ground through the bells at stations M and J. rl`he current in the circuit, just traced is not sultieient'toanse the operation ot marginal relay 253 at this tiine. Both subscribers at stations M and ,l hear the rii'ig'ine' signal, but

the. subscriber at station M reeon'i'iizes the code and answers the call. whereas `the subscriber at J does not recognize the signal as his` and does not answer the call.

Should the calling subscriber asl; t'or a connection with the subscriber at station LI the operator actuates lfeyJ thereby connectingground to contacts Q61, E262 and Q63'. T he closure ot the contacts :Bol causes relay 241.3 to operate in the saine manne' as described in connection with the operation ol ltey M. 'lhe closure ot the contacts 2622 causes relay 25o to operate in a nianner similar to that described in the previous connection. The closure of the contacts 2(53 causes the sleeve relay 2l@ to operate and lock. lt will be noted that when key J" is actuated, relays 252 and Ql do not enter into the ringing operation. 'elays Qel-, Q56 and i210 in operating perform the salue functions as hereinherloro described in connection with the previous signaling operation. A circuit -tor a special codo oi ringingr current nou' trarcrses a path which inay 'be traced troni the ringingl current supply through the inter-- rupter itil, conductor 265, back contact and outer left-hand armature oi relay 2552, lel'tnhand armature and hack contact ot relay Q05), through the Winding' ot marginal relai' 25315, outer lett-hand armature and front con'- tact ot relay 256, it'ront Contact and upper arn'iature ot re ay 245, tip contacts of plug); and jack QUT to ground through the bells at the subst-ribers7 lstations M and fl. The sule'lcriher a, station .l `responds to the nalingA current at this iiniej whereas the sul-i.V scriber M does not heed the signal.

lipon a rennes! 'l'or a party lt" conne"- tion` the operator actuates the lacy lt, thereby connectiup ground to the contacts 2(t 2G? and 26S. 'l`hesa1ne relays which were operated in response to the actuation ol hey lvl" u'ith the exception ol" relay 256, are noir operated so that the path `lor the ringing' current may be traced lroin the ringing current supply through the interruptor QG, conductor 261, 'troni contact and left-hand armature ol' relay troniV contact and, outer le''vhaud armature oi relav lett-hand armature and hach contact of relay 2ML winding oi marginal relay 2525i outer leift-r hand armature and haelt contact oi relai' tiu. troni contact and lower armature ol relay al?)` rina' contacta olt plug :'oi' to ground through the suhseribers` hella al stations .h and W. 'Though the hella at both stations; lt and il' a 'e actuated in response to this signaling; current the subscriber at station il reeoenizes the code as his sional and ansnrers the fall. whereas the, subscriber at il," does not heed the sie'nal. H {'ihouid the calling' subsin'iber request a "party lll" connection, the operator actuales hey lil@ thereupon connecting' ground to the, contacts io and 271 so that only relays 2415 and 2l() oil the ringing relays operaie. the circuit tor these relays now heilig' obvious. i'he r1ng'injr current path niryv noni be traced 'troni the ringing current supply through the interruptor Q64. conductor 2G11 baci: contact and outer letthand arnnitureo'lt relay lett-hand armature and hack contact 'of rel 2051' and jack I y lay209, winding'of marginal relay 253, outer which may be traced over the original ring-' ing current circuit as far as the subscriberis line and then through the transmitter land receiver switchh'ook contacts to ground on f either the ring or tip conductors of the connecting circuit, depending u'ioiiwhether or not, relay 256'was operate This circuit includes' the winding ot marginal relay .253, and due to the fact that the .condenser 272 is short circuited,the resist-ance ot this circuit is suiiiciently reduced so as to permit this rela-y to operate.` Relay 253 in operating opens the locking circuit for relays 245,

Y 256 and 252, releasing them operated,

, thereby restoring the ringing equipment to normah rWhen the called subscriber responds, a circuit for relay 222 is established Whicltin'i'y4 behtraced from grounded battery, through the lower lright-hand Winding 'of repeating coilv201, winding'ot relay 222, back contact and llower armature of relay 245, ring contacts of plug 208 and jack207,

over the closed subscribers line loop, 'tip contacts of jack 207 and plug 208, upper armature and back contact of relay 245 to ground through the uppei right-hand winding. of repeating coil 201. Relay 222m operatii'ig opens the circuit for the supervisory lamp 221, which thereupon is extinguished,

- and establishes a circuit for the slow-'operating relay 220, v,which circuit may be -traced from grounded battery, through the winding of relay 220. lefthand armature vand back Vcontact of slow releasing relay 218, front contact and armature of relay 222 to ground over the contact 216 andl armature`215 of relay 206. Relay 213 released when` relay 222 operated. vRelay 220, operatingm the circuit just traced, connects the high voltage battery 275 to its front Contact and left-hand .armature whereupon currrent therefrom flows momentarily over the -front contact and armature of the slow` to release charge relay 219, sleeve contacts of plug 200 and ]a'cl r 130, frontcontacts and armature 121 ot relay l113, brush 136 and terminal of switch F to ground through thewinding of the message register `magnetr166. The magnet 166 in operating Ion this momentary pulsev causes the message registering device to operate to register the call, Relay 220 'in operating locks to ground on the contact 216 and armature 215 oit relay 206 in order to prevent further registration on this connection. Magnet 166 in operating shunts out part of its winding and thereby increases the flow of current in the other part so that liereafter such magnet will remain energized on s,

the cord circuit battery.- It should be noted that relay 219 is so adjusted as lto hold operateduntil relay 220 has closed its contacts.

It will now be assumed that the conversation between the calling and called subscribrers has terminated and the subscribers have tures reconnects the switch line relay 122 to the switch. At its inner armature, relay 123 opens the holding circuit for slow releasing relay 128, which relay after an interval, re stores -to normal. Relay 128 in retracting its armature, opens theholding circuit for relay 113 which relay releases and also opens the original energizing circuit :tor the ofinornial relay 111, which relay, however, is held'operated to ground at the contacts 129 ofthe of-normal switch 110.

Relay 113 in releasing its left-hand armatures, disconnects the tip, ring land. sleeve brushes 127, 124 and 136 ofthe line iinderl vfrom the multiple answering jacks. At its right-hand armature, relay 113 connects ground to the winding ot the release niagnet- 132 by way of the inner left-hand armature and `front contact ot relay a 111,- whereupon the release magnet 132 operates to restore the line finder to normal position. Then the line finder returns to normal, the off-normal contact's`129 are opened, whereupon vrelay 111 releases disconnecting the release magnet trom ground at theriglit f hand armature of relay 113. The' switch apparatus and all equipment shown in 1 are now inlnor'inal position. Y

VThen the calling subscriber hangs up, the circuit-tor ltheV answering cord supervisory relay 202 is also opened'so that the lamp 202 is lighted over a Ycircuit extending v`trom grounded battery, armature 214 and front contact of relay 206, armature and back contact of relay'202, filament of lamp 201, contacts 217 and 216 and armature 215 of relay 206. vThe illumination ot' lamp 204 at this time serves fas a disconnect signal to the! operator. l

^ `When the called party restores the receiver to nor1nal,`the circuit Jfor the calling super'- visory relay 222 is opened, whereuponlamp 221 is lightedover a circuit extending from. grounded battery through the filament of itl lamp :22h haelt Contact, and armature ol re lay 2:2?, to `ground over the contact 216 and arinaturi-x Elfi ot relayv 20G.

Upon receipt ot a cliseonneet signal, the operator may prot-eetl to take down the eon- .neet'itnr Upon Withdrawine plu.;r :Boll troni iaeli lt) no cord eireuit equipment is atleeted, Sine-e the sleeve eoinluetor ot the aufrufen ing' end olE the cord ia opened lar the releafe olA relaya i202 and '.ll) and by the operation ot relaiY No. The \\'itlnlra\\'al ol plug' tlt vl'roin jaelr :20T eauaes; the opening' et' the lorie ing eirouits lor relay 2li) and 206. llelay 20o in releaaingg` its armatures` opens the eireuitf; :lor the lamps E204, and 221 whereupon these lainps are extinguiahed and alto opens the looking;` eirruit 'for relai' 522). whereupon this relay release?. The oord circuit equipnient it: non` in norinal Condition.

Relay t28 aasoeiatetl with the line liucler lt is n'iatle Slow releasing' so as to enable an operator to remove the ansuc-tring' plug i200 'troln the jael; 130 without causing` the release ot the line linder. vWhen the plug' 200 ig withdrawn 'from jael 11,3() and when the Subscriber at Station A, is on the line, relay 133 releatfes and opens the eireuit for the eut-ott relay '123` which relay thereupon retrat-ta ita arniaturea. ln retraetzingr its inner armature. rela)v '123 opens the holding' eireuit 'tor rela \v 128, but atv its tiro outer armatures-t, relayv 1123 reoonneeta the switch line relay` to the Calling' line and this relay immediately operatea over the rlosed Sub eerihena lino loop. and at ita lett-hand arinature ert'ablishes another holdin;r eireuit: tor relay 12S. n'hieh relayv therefore remains op erated and prerents the release ot rela)Y ll and the subsequent operation ot the release magnet- 132. At its righbhand arn'lature, relayv 1:22 again Causes the illun'iiimtion o'l'I the multiple line lamps. Should the calling' subscriber flash under this condition, relay 122 Will follow the switehhook aetuationa and Cause the flashing' of the line lampo, Relay '128 however, will remain operated to prerent the release ot the line finder.

lt the calling' aubaeriber in the prt-rions: deeorivt-iona requested a eonneetic'in which nee tated the employment ot a truul: Cir* enit wherein no applira tion ol" ringing our rent .ifs reruiired, the operator would insert plug *.108 into the trunk jack :280 o t' the, Se leeted trunk and aetuat'e the trunl; khey rl. The staino relaya which were operated when plug' was inserted into jaelc 20T operate upon the insertion ot the plur- 20S into the trunk jaeli Q80. The eloaure oil contacts 281 ol* lrey T causes relayY Q10 to operate and loeli to the Sleeve ot the calling ond of the eoiineeting circuit, and the diSeonneet-ion ol tho common ringing keys as in the preceding descriptions Without Causing ringing' eur rent to be applied, since no other ringing relays are operated.

20ML) into the aelr 130, alle wouldL be prevei'itedfrom doing' so in the :following nianner. Up-y on the iinerton ot i'ilug); itlt) of the l'irst oord into the giaeli lil-tl. the Sleeves ol the jiaeltv la() and all the nuiltiple jacks heeaine at busyr potential by reason ot the Current flow through the, win-:ling ot relay i205 ol the first cord in Series with the .vinrling,T ot relay 10:2 in the lino circuit. iVhen a seo-ond open ator .inserta one oli her answeril'lg plugs into the jael 140 of the calling line, the battery on the Sleeve thereof causes the test relay 20 oit the second Cord oirouit to operate in a circuit extending' 'troni battery on the, aleere ot jack Il()` sleeve ot the answeringr plus; ot the seeonel Cord, armature 212 and baelr contact-ot relajyv 20G of the Second oord, Winding of test,- relay 203 o1" the Second cord to ground at the back Contact and llower armature ot' the listening' relay 205 ot the Seeondeorcl. The second eorrl test relay Q03 thereupon operates to short circuit the see-V ond eord` aupf-irvieor)i7 relay 202 and prevent its operation. Since relay 202 ot the Second cord Cannot operate, the circuit for the Laeeond eord listening' relay 205 i5 held. opened at; the front Contact of the second (ford relay E202. Therefore7 this relay oannot operate and the Second operators headset cannot be connected to the Calling lino, Under such a Condition, the operator upon receiving no Communication from the calling' Subscriber and noting the dead Condition ot lier headset, realizes that the eall has already been answered and removes her answering* plug' from the multiple jaeli 140.

The jack 1T() is employed in establishing a Connection to the subseribee line A.

That ie claimed is:

l. In a telephone system, a. called line, a plurality ot eonneetingr eireuitaeaeh having; anawerinn' and calling' mide, ringing equip nient including' a plurality ol.' keys eonnnon to said connecting' eireuit'a, ineana responsire to the Connection ot the Calling end o t Said Connecting eireuit with the ea llecl line tor operatively7 associating sai-rl ringing' equipment with the eonneet'ing eireuit our ployed, a source ot ringingcurrent, means 1'es1 ioiir-'irey to the actuation, ot one of said keys; for transmitting current; 'troni said source over said connecting; eireuitand diaeonneeting said eonnnon ringingr equipment: from said connecting: eirouitj and ineana responsive lo the actuation ot another ol' Said keys lor disconnecting; sai-d eonunon ringing;` equipment from .Caid lino and prerenting the tranainiaaion of current 'trom said source.

In n telephone system, a eallecl line,` a

connecting circuit havin-g answering and calling ends, a plurality of keys for said tion of current from said sourceto said connecting circuit and disconnecting said keys therefrom, one of saidlocking relays being also individually responsive to the actua tion of another of said keysy for preventing the' operation of the other of said locking relays.

3. In a telephone system, al calling line, a called line, a plurality oi connecting circuits having answering and calling ends, an operators set common to said connecting circuits, ringing control equipment common to said connecting circuits, a relay for each ot' said connecting circuitoperated in response to the connection of the answering end of one of said connecting circuits with said'calling line, and a secon-d relay responsive t0 the operation of said first relay for connecting said telephone set with said connecting circuit, and means responsive to the connection of theother end of said connecting circuit with said called line for operatively associating said ringing control equipment with the calling end of said connecting circuit and 'for causing said second relay to release to disconnect said telephone set 'from said connecting circuit.

In testimony whereof, I have signed my.y

name to this specification this 7th day of February, 1925.

RAND s. BAILEY. 

